Radiation and Atomic Structure of Helium

Common Radiation

• Energy transmission occurs via particles or waves.
• Ionizing radiation includes X-rays, Bremsstrahlung, characteristic X-rays, gamma radiation, annihilation radiation, positrons, electrons, protons, neutrons, alpha particles, and other heavy ions.

Atomic Structure of Helium

• Helium's subatomic structure consists of 2 protons, 2 neutrons, and 2 electrons.
• Protons have a large positive charge and mass, defining the element.
• Neutrons have similar mass to protons but no charge.
• Electrons are significantly lighter than protons and have a negative charge. Electrons orbit the nucleus.

Alpha Radiation

• Alpha particles are identical to helium-4 nuclei, comprising two protons and two neutrons.
• Alpha radiation is often produced during alpha decay.
• They can also be written as He²⁺ (identifying the loss of two electrons).
• In their environment, alpha particles gain electrons, becoming electrically neutral helium atoms.

Beta Radiation

• Beta particles are high-energy, high-speed electrons or positrons.
• Beta decay occurs within radioactive atomic nuclei and emits beta particles.
• Two forms exist: beta- decay and beta+ decay.

Gamma Radiation

• Gamma radiation is electromagnetic radiation.
• Gamma rays have higher energy and shorter wavelength than X-rays; frequencies above 10¹⁹ Hz.
• These energies are greater than 100 keV, and shorter wavelengths than the diameter of an atom.

X-rays

• X-rays have low energy (120 eV to 120 keV)
• They have shorter wavelengths than ultraviolet, and longer than gamma rays.
• They are also called Röntgen radiation, after Wilhelm Conrad Röntgen.
• X-ray production in a tube involves high voltage to accelerate electrons toward a target.
• The higher the target atom number, the higher the X-ray yield and the higher the incident electron energy results in increased X-ray production probability.
• X-ray production decreases with increasing X-ray energy.

Neutron Radiation

• Neutron radiation is a stream of free neutrons.
• Neutrons react with nuclei of other atoms; resulting in the formation of new isotopes and chain reactions.
• Neutron radiation can result in nuclear fission or fusion.
• This radiation is dangerous and harmful over large areas.
• Neutron properties include composition (two down quarks, one up quark), rest mass, energy equivalent, an electric charge of zero, and a half-life.
• Decay schemes of their radioactive decay is described.

Neutron Sources

• Different neutron sources generate neutrons through various methods:
• Californium-252 sources: Generate neutrons via alpha decay and fission.
• (α, n) sources: Mix a source like Ra-226 with light elements like Be.
• (γ,n) sources: Mix a higher-energy gamma source with light elements.
• Neutron Generator: Accelerate particles to generate neutrons ( D-D and D-T reactions).
• Specific sources have varying half-lives, neutron energies, and fluence rates (commonly expressed in n/cm²/s).

Measuring Neutron Source Strength

• Neutron emission rates for alpha, gamma, and spontaneous fission neutron sources are measureable through the manganese sulfate bath technique.
• The resulting neutron emission rate is calculated through gamma spectrometry of the Mn-56 product.
• Detecting neutron leakage improves emissions calculations.

Alpha Neutron Sources (types)

• AmBe, PuBe, and RaBe sources comprise specific mixes of radioactive isotopes and materials.
• These sources showcase characteristics such as yield, half-life, average neutron energies, and associated gamma dose rate and neutron dose rate measurements.

Alternatives to Beryllium

• Beryllium is the most common low-Z material, and other materials like fluorine, lithium, and boron are alternatives to beryllium.
• These alternatives have different neutron energies.

Source Construction

• Alpha emitters and beryllium materials are intimately mixed (alpha emitter oxide + beryllium metals) and compressed into cylindrical shapes for encapsulation.
• Double encapsulation with stainless steel is common to contain the source well.

Gamma Neutron Sources

• Sources have high gamma activity, and neutrons are close to being monoenergetic.
• The primary disadvantage is the high gamma emission rate. Gamma-emitting core surrounded by the target material.
• Examples include antimony-beryllium sources, with an antimony core activated in a reactor.